Short antenna array with director mounted coaxially on dipole



Sept. 30, 1969 K. FRAY 3,470,560

SHORT ANTENNA ARRAY WITH DIRECTOR MOUNTED COAXIALLY ON DIPOLE Filed Aug. 10, 1966 2 Sheets-Sheet l FIG. 1

INVENTOR xmssuzv FRAY ATTORNEYS snon'r ANTENNA ARRAY WITH DIRECTOR MOUNTED COAXIALLY oN DIPOLE Filed Aug. 10, 1966 K. FRAY Sept. 30, 1969 2 Sheets-Sheet I? INVENTOR KI NGSLEY PRAY BY f ATTORNEYS United States Patent 3,470,560 SHORT ANTENNA ARRAY WITH DIRECTOR MOUNTED COAXIALLY ON DIPOLE Kingsley Fray, Ellenville, N.Y., assignor, by mesne assignments, to Avnet, Inc., New York, N.Y., a corporation of New York Filed Aug. 10, 1966, Ser. No. 571,450 Int. Cl. H01q 21/12, 15/14 US. Cl. 343-815 11 Claims ABSTRACT OF THE DISCLOSURE An end-fire antenna array, including high band and low band antennas for use, respectively, with the UHF and VHF television receiving bands. Each of these antennas comprises an array of dipoles with the UHF an tenna being arranged in front of the VHF antenna. Parasitic director elements are associated with the VHF band antenna and intended primarily to operate over the upper VHF band. These parasitic directors are interleaved with the elements of the UHF antenna, but mounted to the sides thereof so as not to appreciably affect performance of the UHF antenna over its operating band. Each of such parasitic directors may be mounted at an extremity of a UHF dipole element and insulated therefrom by conventional means.

The present invention pertains to antennas, and, in particular, to television receiving antennas operable over both very high frequency (VHF) bands and the ultra high frequency (UHF) band presently allotted to commercial television broadcasting.

VHF television transmission occurs over a relatively wide frequency range which is broken up into two separate bands. Thus, channels 2 through 6 broadcast on frequencies between 54 and 88 megacycles (exclusive of the band between 72 and 76 megacycles), and channels 7 through 13 utilize carrier frequencies between 174 and 216 megacycles. The UHF frequencies comprise a third distinct band which extends from 470 to 890 megacycles, corresponding to channels 14 through 83.

Commercial television receivers are now generally equipped with both UHF and VHF tuners to enable reception of channels 2 through 83. However, there are no commercially feasible antennas capable of receiving so wide a frequency band, and, from a practical viewpoint, it is virtually mandatory to employ separate antennas for UHF and VHF reception thereby introducing various problems in electrically coupling the antennas to the receivers as well as problems relating to the mechanical construction of the array.

It is known that some of the problems inherent in the use of separate antennas for the UHF and VHF bands may be reduced by properly arranging the two antennas on a single horizontal boom, and utilizing a single down lead from the overall array to the television receiver. However, to achieve this objective, the length of the overall array may sometimes reach unwieldy proportions, particularly where it is desirable to employ additional parasitic director elements with the VHF antenna for increased gain. This is due to the fact that if an effective VHF parasitic element is placed in front of one or more of the active elements of the UHF section (assuming the array is an end-fire array toward the front), it will behave as a reflector at UHF frequencies thereby ruining performance of those UHF element(s). Thus, the minimum length of such prior art arrays has heretofore generally been approximately equal to the sum of the lengths of the UHF and VHF antenna sections. For practical rea sons pertaining to the cost, assembly and maintenance of commercial television antenna arrays. it is desirable to "ice reduce the length of such arrays without injuriously affecting the electrical behavior of such arrays.

Accordingly, the main object of the present invention is to provide an antenna array useful over a plurality of frequency bands wherein the length of the array is substantially less than equivalent prior art constructions.

Another object of the invention is to provide an antenna array in which portions of at least two antenna arrays, each operable over a discrete frequency band, may be interleaved in substantially the same horizontal plane without detrimentally affecting performance.

A more specific object of the invention is to provide an antenna array of particular utility in receiving the UHF and VHF television bands, the array being substantially shorter than electrically equivalent prior art arrays.

Briefly, the objects of the invention are achieved by physically combining a UHF antenna in such a fashion that at least some of the parasitic elements of the VHF antenna are physically located at the sides of the UHF antenna. Preferably, this is achieved by attaching at least one of such parasitic elements to one of the active UHF elements, and separating the two by means of a suitable insulator. Accordingly, although a VHF parasitic element is interleaved with the UHF portion of the antenna, the parasite is physically located to the side (as opposed to in front) of the active UHF antenna elements, and therefore the parasite does not appreciably affect the performance of the UHF antenna.

The preferred embodiment of the invention pertains to a combined UHFVHF television receiving antenna, and, accordingly, the specification and drawings are specifically directed to such an antenna. However, the principles of the invention are not limited to particular frequency ranges or, for that matter, to receiving antennas, and would be applicable to any antenna array which must operate over wide or discrete frequency bands.

The manner in which the above and other objects of the invention are accomplished is more fully described below with reference to the attached drawings, wherein:

FIGURE 1 is a top plan view of an antenna array according to the invention;

FIGURE 2 is a side view of the antenna array of FIG. 1, but omitting the rear portion thereof;

FIGURE 3 is a bottom view of the UHF portion of the antenna; and

FIGURE 4 is a sectional view along the line 44 of FIGURE 2.

Referring to the drawings, a vertical. mast is shown at 10 to which a horizontal boom 11 is attached by a conventional bracket 12. The down lead of the antenna is shown at 13 and may be coupled to a suitable UHF-VHF converter, which relays the received signals to the television receiver, or directly to the receiver. The. active portions of the VHF and UHF antenna sections are shown generally at 14 and 15 respectively.

The active portion of the VHF antenna section includes, for example, four active dipole elements 18, 19, 20 and 21, each having a respective close-spaced short parasitic element 22, 23, 24 or 25 associated therewith. Dipoles 18 to 21 decrease in length toward the front of mounted on an insulated block 28 riveted or otherwise suitably secured to boom 11 as shown at 30. The parasites 22 to 25 are similarly mounted, as on insulated blocks 32, by respective rivets 34 or the like.

The active elements 18 to 21 are connected to a transmission line harness comprising conductors 36 and 38 having a line transposition between each pair of adjacent dipoles. This construction, as so far explained is an endfire array and forms the subject matter of US. Reissue Patent No. 25,604 for End Fire Planar Dipole Array With Line Transposition Between Dipoles and Impedance Increasing Towards Feed, issued June 16, 1964, to Greenberg; therefore its operation need not be explained in detail. Briefly, one or more of the dipoles 18 to 21 are effective in a half-wave mode at all of the channels in the low VHF band. In the high VHF band, the dipoles act in a three-halves-wave mode with the parasites 22 to 25 providing the desired directivity and impedance relationship among the respective dipoles. One of the highly desirable characteristics of this antenna array is that at each channel of the VHF bands, it is highly directive, with the direction of greater effectiveness extending from the front end of the antenna. In the following description and claims, the front of an antenna refers to the end from which the direction of greater effectiveness extends.

The elements of the active portion of the UHF antenna section 15 comprise three dipoles 41, 42 and 43 suitably supported on the bottom of the boom 12 by U-shaped insulators 44 or other conventional means. A transmission line 46, 48 is electrically connected in sequence to each of the dipoles 41, 42 and 43 (by riveting, for example) with no line transposition between the adjacent dipoles. Transmission line 46, 48 includes respective terminals 50 and 52 which are connected to the down lead 13 so that the active portion of the UHF antenna 15 is fed from the rear (i.e dipole 43). In accordance with known principles, this provides a highly directive antenna which also has its direction of greater effectiveness extending toward the front of the array. As shown, the dipole 42 is mounted beneath transmission line 46, 48 and thus slightly beneath the plane of dipoles 41 and 43. A U-shaped insulator 53 is clamped to the support 44 of dipole 42 by wing nut screws 55 to connect the transmission line 46, 48 to dipole 42 and to mechanically brace the line.

The UHF transmission line 46, 48 is coupled from the front of the UHF antenna section (i.e. dipole 41) via properly matched line 54, 56 to a transmission line 58, 60 mounted on top of the boom and extending back into a conducting relationship with the respective halves of dipole 18, ie the front dipole of the VHF antenna section. The transmission line 58, 60 may comprise metallic tubes or rods mounted by any conventional means, as on insulating blocks 62 and 64. Directors 65a and 65b may also be suitably mounted on boom 11 in front of dipole 41 to increase the effectiveness of the array from the front end at the UHF frequencies.

The UHF and VHF sections of the array perform highly satisfactorily in a known fashion, but it may nevertheless be desired to add additional parasitic elements in front of the active VHF portion 14, particularly to improve performance on the high VHF band. For this purpose, it is known to use one or more parasitic elements spaced approximately one foot in front of the front dipole 18 to serve as a director at the high VHF band. In accordance with the prior art, no element of the active UHF portion 15 could be located in the space between the VHF director and dipole 18 since an effective director, even at the high VHF band, must be more than one-half wavelength at all frequencies in the UHF band. Therefore, as is well known, such a director would behave as a reflector with respect to the active elements of the UHF antenna within such space, thereby rendering these active elements ineffective. In accordance with the invention, however, it is now possible to locate one or more of the active elements of the UHF antenna in the space between the active VHF antenna portion and its director(s).

Thus, two parasitic elements 66 and 68 are mounted at opposite ends of one of the dipoles, for example, dipole 42, of the active UHF antenna portion 15, and spaced therefrom by suitable insulators 70 and 72. The mechanical connections between the parasites 66 and 68, insulators 70 and 72, and dipole 42 may be made in any conventional manner, as shown schematically by clamps 74. With this construction, the parasitic elements 66 and 68 will not :be in front of any of the UHF active elements during operations on the UHF band and yet they are sufficiently spaced with respect to the VHF antenna portion to serve as conventional directors thereby improving the directivity of the array on the high VHF band. To some extent, each half of dipole 42 will also act as a director, but their effect will not be great because of their relatively short lengths. The lengths of directors 66 and 68 will be determined essentially in accordance with conventional criteria. To some extent in the illustrated embodiment, the lengths will slightly be shortened due to end loading to the adjacent conductors of dipole 42, :but this difference will amount to less than one inch in this embodiment.

The antenna behaves electrically in the same fashion as a prior art antenna which would be physically longer by approximately one foot. This saving in space is extremely important from a practical viewpoint particularly in metropolitan and suburban areas and, of course, may become even more important in situations Where it would be desirable to use more than a single director. In such a case, the additional directors could be added to the UHF active elements in the same manner as elements 66 and 68 were added to dipole 42.

For purposes of example only, the following table is offered setting forth the preferred lengths of the elements illustrated in FIGURES 1 through 4, as well as the respective distance between such elements:

LENGTHS Tip to tip length Element: in inches Dipole 18 5O Dipole 19 70 Dipole 20 Dipole 21 Parasite 22 26 /2 Parasite 23 26 /2 Parasite 24 27 Parasite 25 28 /2 Dipole 41 15 Dipole 42 16 /2 Dipole 43 18 Parasite 66 24 /2 Parasite 68 24% Director 65a 6 Director 65b 6 SPACING Distance: Inches Director 65a to director 65]) 2% Director 6512 to dipole 41 2% Dipole 41 to dipole 42 3% Dipole 42 to dipole 43 4 Dipole 43 to parasite 22 4% Parasite 22 to dipole 18 3 Dipole 18 to parasite 23 9 Parasite 23 to dipole 19 3 Dipole 19 to parasite 24 8 /2 Parasite 24 to dipole 20 3 /2 Dipole 20 to parasite 25 8 Parasite 25 to dipole 21 4 Those skilled in the art will recognize that numerous modifications of the illustrated embodiment may be made within the scope of the invention. For example, the principles of the invention obviously are not limited to front or rear fed antennas, or for that matter, to particular forms of VHF and/or UHF antennas. As mentioned previously, the invention also is not limited to antennas cut to any particular frequency range or ranges. Furthermore, it is not mandatory that the parasites 66 and 68 (or their equivalents) be mounted at the side of the higher frequency antenna portion by direct mounting on an active element of the high frequency antenna. For example, if desired, such directors could be suitably 75 mounted on non-conductive bars extending outwardly from the boom at a suitable point within the UHF antenna portion. Moreover, as shown in the preferred embodiment, the respective antenna portions need not be in the exact same horizontal plane, the invention being applicable in any case wherein the director for one portion of the array would behave as a reflector (or otherwise deleteriously affect performance) over another portion of the operating frequency band. Also, the invention may be applied to antennas wherein the side-mounted parasite has some slight effect on the directivity of the high frequency portion of the antenna at one or more operating frequencies, as long as satisfactory performance occurs and the antenna length may be substantially reduced.

Accordingly, the invention should not be limited except as defined in the following claims.

What is claimed is:

1. An end-fire antenna array, comprising high band and low band antennas operable at upper and lower frequency bands respectively, said antennas each having a direction of greater effectiveness extending from the front of the antenna array, said antennas each including active portions, the active portion of said high band antenna being positioned in front of the active portion of said low band antenna, at least one parasitic director associated with said low band antenna and spaced forwardly thereof for increasing the effectiveness of said low band antenna toward the front of the array at at least one operating frequency, at least one active portion of said high band antenna being as far forward of said low band antenna as said parasitic director, and means mounting said parasitic director directly to the side of said one active portion of said high band antenna at a location where said director does not substantially change the effectiveness of said high band antenna at the operating frequencies thereof.

2. An end-fire antenna array according to claim 1, wherein said high band antenna comprises at least one dipole element, and said mounting means includes means for mechanically connecting said parasitic director to one extremity of said dipole element, and means for electrically insulating said parasitic director from said dipole.

3. An end-fire antenna array according to claim 2, including at least one other parasitic director, and means for mechanically connecting said other parasitic director to the extremity of said dipole element opposite said one extremity.

4. An end-fire antenna array according to claim 3, wherein each of said parasitic directors is longer than said dipole element.

5. An end-fire antenna array according to claim 1, wherein each of said active portions comprise a plurality of active dipole elements arrayed in file in horizontally spaced relation, a transmission line connected to each of said active dipole elements, and means for connecting a signal transmission line to an active dipole element at an end of one of said active portions.

6. An end-fire antenna array according to claim 5, wherein said mounting means includes means for mechanically connecting said parasitic director to one extremity of one of the dipoles of the high band active portion, and means for electrically insulating said parasitic director from said one dipole.

7. An end-fire antenna array according to claim 6, including at least one other parasitic director, and means for mechanically connecting said other parasitic director to the extremity of said one dipole element opposite said one extremity.

8. An end-fire antenna array according to claim 7, where each of said parasitic directors is longer than the longest of said high band dipole elements and shorter than the shortest of said low band active dipole elements.

9. An end-fire antenna array according to claim 8, wherein said transmission line includes a line transposition between each active dipole element of the low band antenna and its rearwardly adjacent active dipole element and wherein said signal transmission line connecting means is connected to an active dipole element at an end of said high band active portion.

10. An end-fire antenna array according to claim 9, wherein said last-named active dipole element is the rearmost active element of said high band active portion.

11. An end-fire antenna array, comprising high band and low band antennas operable at upper and lower frequency bands respectively, said antennas each having a direction of greater effectiveness extending from the front of the antenna array, said antennas each including a plurality of active dipole elements, the active elements of said high band antenna being positioned in front of the active elements of said low band antenna and signal transmission means electrically connected to said dipole elements for coupling said array to other apparatus, said signal transmisison means comprising (a) means for connecting a signal transmission line to the rear-most of said high band dipole elements, and (b) a transmission line connecting the front-most of said high band dipole elements to the front-most of said low band dipole elements.

References Cited UNITED STATES PATENTS ELI LIEBERMAN, Primary Examiner US. Cl. X.R. 343-9l2 Patent N0. 3 470 ,560 Dated Sept 30 l 1969 Inventor(s) Fray It is certiiied that error appears in the above-identified patent and that szlid Letters Patent are hereby corrected as shown below:

r Col. 2, after line' 61, insert -the array (i.e. toward dipole l8) and each is suitably-'- SIGNED AND SEALED JUN9 1970 E .Auest:

Edward M. Fletcher, Ir. 1AM E 60m, m. Attesting Officer commissioner or Pawn 

